A carrier network generally refers to a computer network through which users communicate with various service providers (e.g. Internet web servers). Carrier networks include “Shared Access Carrier Networks,” in which data of multiple users are conveyed together over a shared communications medium between the users and an intermediate network. One of the most prevalent Shared Access Carrier Networks today is found in the Data-Over-Cable (DOC) Network, which includes traditional networks constructed from coaxial cable and hybrid fiber coaxial (HFC) networks constructed with both fiber optical cabling and coaxial cable. Other Shared Access Carrier Networks include wireless and digital subscriber line (xDSL) networks (the xDSL lines typically being aggregated onto an oversubscribed backhaul trunk into the Intermediate Network, with the trunk defining the shared communications medium).
In conventional shared access carrier networks such as a hybrid fiber coaxial (HFC) network, a bidirectional communication path is maintained between a network headend and each remote point in the network. The communication path simultaneously carries broadband radio frequency (RF) signals in two directions on the same medium by dividing the frequency spectrum of the bidirectional communication path. Frequency division multiplexing (FDM) allows two or more simultaneous and continuous channels to be derived from a shared access transmission medium. FDM assigns separate portions of the available frequency spectrum to the “downstream” or “forward path” direction from a headend signal source to a plurality of remote points, and a second frequency range for carrying signals in the “upstream” or “return path” direction from each remote point to the headend.
For example, a conventional cable modem system provides a point-to-multipoint topology for supporting data communication between a cable modem termination system (CMTS) at a cable headend and multiple cable modems (CMs) at the customer premises. In such systems, information is broadcast on downstream channels from the CMTS to the cable modems as defined in DOCSIS in accordance with a time division multiplexing (TDM) technique. In contrast, information is transmitted upstream from each of the cable modems to the CMTS on the upstream channels as short burst signals in accordance with a time domain multiple access (TDMA) technique. The upstream transmission of data from the cable modems is managed by the CMTS, which allots to each cable modem specific slots of time within which to transfer data.
Network carriers and their equipment providers have adopted industry standards in order to increase interchangeability and reduce manufacturing costs for network hardware. For example, DOC carriers have adopted industry standards such as the Data Over Cable Service Interface Specification (DOCSIS). DOCSIS version 1.0 was issued in 1997 with hardware devices being certified starting in 1999. DOCSIS version 1.1 replaced version 1.0 in 1999-2001 and now accounts for the bulk of installed DOC network equipment. Although released, DOCSIS version 2.0 is not yet widely available. As a result, networks conforming to DOCSIS (i.e. DOCSIS-compliant) use DOCSIS version 1.1 hardware in most cases. In part, DOCSIS sets forth requirements and objectives for various aspects of cable modem systems including operations support systems, management, data interfaces, as well as network layer, data link layer, and physical layer transport for data over cable systems.
Since the number of upstream time slots available in a DOCSIS compliant shared access carrier system is limited, the number of cable modems that can register and communicate over the system is also limited. In part as a result of the continuing rapid growth of the Internet and the need for broadband access to it, the number of cable modems seeking access to the shared access carrier system can readily exceed the available resources of the system.